The present invention relates to integrated circuit (IC) fabrication technology, and more particularly, to a method of fabricating an IC having a sealed cavity.
Some products use packaging technology that involves bonding a cap over a predetermined area of a substrate to create a hermetically sealed cavity. The hermetically sealed cavity is often formed to protect sensitive circuit elements therein. FIG. 1 is a perspective illustration of a sample apparatus 10 including a device chip 20 having a substrate 22 and circuit elements 24 fabricated on the substrate 22. A cap 30 is attached, via thermo compression bond, over the device chip 20 defining a hermetically sealed cavity within which the circuit elements 24 are protected.
FIG. 2 illustrates a cut-away side view of the apparatus 10 of FIG. 1 after the bonding process. The hermetically sealed cavity is indicated with reference number 26. As illustrated, bottom of the hermetically sealed cavity 26 is defined by the device chip 20 including the substrate 22 and the circuit elements 24. Top of the hermetically sealed cavity 26 is defined by the cap 30. The sizes of the device chip 20 and the cap 30 can vary greatly depending on implementation but can be, for example, on the order of millimeters (mm) or fractions of millimeters, for example, about 0.5 mm to 2 mm.
Sides of the hermetically sealed cavity 26 are defined by gasket 32 which can be a part of the cap 30. The gasket 32 is attached to the substrate 22 using bonding agent 34 such as gold. To achieve the hermetically sealed cavity 26, the bonding agent 34 is applied to the substrate 22, the gasket 32, or both before they are brought together. As for the bonding metal 34, gold (chemical symbol Au) is often used but other materials can be used as the bonding agent. Then, the device chip 20 and the cap 30 are pressed together and heated to effectuate diffusion bonding. The gasket 32 can be about 1 to 10 microns thick depending on implementation. This process results in a hermetic sealing of the cavity 26; however, long-term exposure to harsh environmental conditions such as high temperature, high humidity, or both can lead to corrosion and leaking of the bond agent thus losing the hermeticity of the cavity.
Accordingly, there remains a need for a method of manufacturing an apparatus with sealed cavity that provides even higher level of protection against adverse environmental conditions.